Floor covering

ABSTRACT

Hard panels formed from a wood-based material and having a decorative layer for floor coverings are provided, at least on two opposite edges, with coupling devices made in one piece with the panels wherein similar panels may be coupled together to form a floor covering, wherein these coupling devices provide for an interlocking in a direction perpendicular to the plane of coupled panels, as well as in a direction perpendicular to the edges concerned and parallel to the plane of coupled panels. These coupling devices are constituted of a tongue and a groove. The top side of the tongue has a protrusion that cooperates with a meshing recess located in the lower side of the upper lip of the groove of the coupling devices, and a portion extending generally parallel with the plane of the panel to form a contact surface cooperating with the lower side of the upper lip of the groove.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 11/979,317filed Nov. 1, 2007, now U.S. Pat. No. 7,779,597, which is a divisionalof application Ser. No. 10/890,456 filed Jul. 14, 2004, now U.S. Pat.No. 7,343,717, which is a divisional application of application Ser. No.09/878,206 filed Jun. 12, 2001, now U.S. Pat. No. 6,772,568.

FIELD OF THE INVENTION

The present invention concerns panels for making a floor covering, inparticular of the type consisting of hard panels.

In particular, it concerns laminate panels, also called laminateparquet.

BACKGROUND OF THE INVENTION

It is known that such laminate panels can be made of different layers.Usually, the panels are formed of boards having a wood basis, such aschipboard or fiberboard, in particular MDF (Medium Density Fiberboard)or HDF (High Density Fiberboard), upon which one or several layers,including a decorative layer, are provided at least on the top side. Thedecorative layer may be a printed paper layer, but in certainembodiments it may just as well be a layer of wood, in particularveneer. Such panels can also be made of other materials, for examplemerely synthetic material, or of a base plate on the basis of wood, suchas chipboard, MDF or HDF and the like, upon which is provided, insteadof a printed paper layer or veneer, another material such as cork, thinstrips of wood and the like.

It is also known to couple these panels on their edges as they are laidto form a floor covering, either by means of a conventional tongue andgroove joint, whereby they are possibly glued together, or by means of aglueless coupling which provides for a mutual interlocking of the panelsboth in the horizontal and vertical directions, for example as describedin U.S. Pat. No. 6,006,486.

The present invention relates to hard panels for floor coverings, inparticular laminate panels, which provides for new embodiments accordingto different aspects offering respective advantages.

BRIEF DESCRIPTION OF THE INVENTION

According to a first aspect, the invention provides for a floor coveringpanel comprising a hard panel, wherein the panel is provided, at leaston two opposite edges, with coupling means made in one piece with thepanel, so that several of such panels can be mutually coupled, wherebythese coupling means provide for an interlocking in a directionperpendicular to the plane of the coupled panels (vertically active), aswell as in a direction perpendicular to the edges concerned and parallelto the plane of the coupled panels (horizontally active), whereby saidcoupling means comprise a tongue and a groove and whereby the lip whichis situated on the bottom side of the groove, hereafter called the lowerlip, is longer than the lip on the top side, hereafter called the upperlip, wherein the edge which is provided with the tongue, is madeflexible.

As the edge onto which the tongue is provided is elastically flexible,deflections arising during the coupling of the panels are accommodatedby this edge, and the above-mentioned upper lip is safeguarded againstlarge deflections, as a result of which the material cannot possiblysplit due to the bending of the lower lip.

The lower lip is preferably even made rigid, by making it sufficientlythick, so that any bending in this lip is entirely excluded.

According to a first possibility, the above-mentioned flexibility isobtained by making at least the tongue elastically flexible. Accordingto a second possibility, which is preferably combined with the firstone, and which contributes even more to the required flexibility beingobtained, the tongue is situated on a part which is connected to theactual panel via a flexible zone in the shape of a local constriction.

Specific advantages of the embodiment according to the first aspect arefurther explained in the following detailed description.

The coupling means are preferably made such that they allow the panelsto be coupled by pushing them laterally towards one another.

According to a second aspect, the invention provides for hard panels forforming a floor covering, wherein the panels are provided with couplingmeans on at least two opposite edges, as a result of which several ofsuch panels can be mutually coupled to one another, wherein thesecoupling means provide for an interlocking in a direction perpendicularto the plane of the coupled panels, as well as in a horizontal directionperpendicular to the edges concerned, and parallel to the plane of thefloor panels, wherein said coupling means comprise a tongue and a grooveand whereby the lip situated on the bottom side of the groove, hereaftercalled the lower lip, is longer than the lip on the top side, hereaftercalled the upper lip, characterized in that the coupling means consistat least of first coupling parts, formed of contact surfaces working inconjunction with one another, on the top side of the tongue and thebottom side of the upper lip respectively; second coupling parts formedof contact surfaces, on the top side of the lower lip and an oppositepart of the other panel respectively; and third coupling parts providingfor the horizontal interlocking in the plane of the coupled panels andwhich are situated on the lower lip, yet further than the free end ofthe upper lip, wherein these third coupling parts are situated betweenthe first and second ones.

As a result, the vertical forces which are created when walking over thefloor covering are divided over two places, which results in a betterdistribution of the forces.

The third coupling parts preferably consist of an inwardly directedcontact surface provided near the free end of the lower lip, on thislip, and a contact surface working in conjunction with it which isformed on the other similar panel to be coupled.

The second coupling parts preferably consist of a contact surface formedon the top side of the free end of the lower lip, as well as a contactsurface working in conjunction with it on the bottom side of the otherpanel.

Moreover, a free space is preferably provided under the tongue extendingfrom the tip of the tongue up to the third coupling parts. As a result,the tongue can be put more easily in the groove, without having to takevery precise tolerances into account.

According to a third aspect, the invention provides for a floor coveringhard panel, wherein the panel is provided with coupling means on atleast two opposite edges, so that several similar ones of such panelscan be mutually coupled, wherein these coupling means provide for aninterlocking in a direction perpendicular to the plane of coupledpanels, as well as in a direction perpendicular to the edges concernedand parallel to the plane of coupled panels, said coupling meanscomprising a tongue and a groove and wherein the lip which is situatedon the bottom side of the groove, hereafter called the lower lip, islonger than the lip on the top side, hereafter called the upper lip,further wherein that the coupling means consist at least of firstcoupling parts formed of contact surfaces working in conjunction withone another, on the top side of the tongue and the bottom side of theupper lip respectively; second coupling parts formed of contactsurfaces, on the top side of the lower lip and an opposite part of theother coupled panel respectively; and third coupling parts which providefor the horizontal interlocking situated on the lower lip, yet furtherthan the free end of the upper lip, whereby the second coupling partsare situated between the first and the third ones, and whereby thesesecond coupling parts consist of contact surfaces working in conjunctionwith one another and defining a local contact zone situated in themiddle or practically in the middle between the tip of the tongue andthe third coupling parts.

By making use of such a local contact zone, there remains a spacebetween this zone and the tip of the tongue, on the bottom side of thelatter, which makes sure that there is freedom of movement for thetongue when the panels are joined.

According to a fourth aspect, the invention provides for a floorcovering hard panel, wherein the panel is provided with coupling meanson at least two opposite edges made in one piece with the panel, as aresult of which several of such panels can be mutually coupled to oneanother, whereby these coupling means provide for an interlocking in adirection perpendicular to the plane of the coupled panels, as well asin a direction perpendicular to the edges concerned, and parallel to theplane of the coupled panels, wherein said coupling means comprise atongue and a groove, further wherein the lip situated on the top side ofthe groove, hereafter called the upper lip, is longer than the lipsituated on the bottom side of the groove, hereafter called the lowerlip, and in that the above-mentioned coupling means contain couplingparts which provide for the interlocking in the horizontal direction inthe plane of coupled panels, wherein these coupling parts consist atleast of contact surfaces working in conjunction with one another,provided on the bottom side of the upper lip, outside the distal end ofthe lower lip, and on the opposite part of the edge of the other panelrespectively.

As the interlocking takes place on the upper lip, it is easier to checkthe reliability of the interlocking while the floor is being laid thanin the case where the interlocking takes place on the lower lip.

According to a fifth aspect, the invention provides for a floor coveringpanels comprising hard panels, whereby each panel is provided withcoupling means on at least two opposite edges made in one piece with thepanel, as a result of which several of such panels can be mutuallycoupled to one another, whereby these coupling means provide for aninterlocking in a direction perpendicular to the plane of the coupledpanels, as well as in a horizontal direction perpendicular to the edgesconcerned, and parallel to the plane of the coupled panels, whereby saidcoupling means comprise a tongue and a groove, and wherein the lipsituated on the top side of the groove, hereafter called the upper lip,is longer than the lip situated on the bottom side of the groove,hereafter called the lower lip, and in that the above-mentioned couplingmeans contain coupling parts which provide for the interlocking in thehorizontal direction, whereby these coupling parts make it possible forthese panels to be mutually disconnected by turning them down towardtheir bottom sides and towards one another.

Thanks to the use of coupling means which make it possible for thepanels to be disconnected by turning them downward, and preferably to beexclusively disconnectable by this movement, the panels fit particularlytight on the coupling means concerned, and are pushed even closertowards one another when being walked on.

The panels are hereby preferably rectangular, and they are provided withcoupling means on two pairs of edges which make it possible for thepanels to be disconnected by means of an upward rotation in order to beunlocked, whereas, on the other pair of edges, as mentioned above, theyare provided with coupling means which only allow for a disconnection byturning the coupled panels with their bottom side towards one another.Also the opposite turning movements increase the guarantee that such acoupling remains always available.

It should be noted that in the case of longitudinal panels, the couplingmeans which allow for a disconnection by turning the panels upward arepreferably provided on the longitudinal sides, whereas the couplingmeans which allow for a disconnection by turning the panels down, arepreferably provided on the shortest sides.

According to a sixth aspect, the invention provides for floor coveringpanels wherein the panels are provided with coupling means on at leasttwo opposite edges made in one piece with the panels, as a result ofwhich several of such panels can be mutually coupled to one another,whereby these coupling means provide for an interlocking in a verticaldirection perpendicular to the plane of the coupled panels, as well asin a horizontal direction perpendicular to the edges concerned andparallel to the plane of the coupled panels, wherein said coupling meanscomprise a tongue and a groove, and further wherein the interlocking inthe horizontal direction is at least provided by coupling parts in theshape of a local protrusion in the top side of the above-mentionedtongue, which meshes in a recess in the lip which borders the top sideof the groove.

An advantage of this embodiment consists in that, since the protrusionis local, the recess can also have relatively small dimensions, and theupper lip is only weakened locally.

According to the sixth aspect, there is preferably no interlocking inthe horizontal direction on the lower lip.

According to a seventh aspect, the invention provides for hard floorcovering panels, wherein the panels are provided with coupling means onat least two opposite edges made in one piece with the panels, as aresult of which several of such panels can be mutually coupled to oneanother, wherein these coupling means provide for an interlocking in avertical direction perpendicular to the plane of the coupled panels, aswell as in a horizontal direction perpendicular to the edges concernedand parallel to the plane of the coupled panels, and whereby:

-   -   the above-mentioned coupling means comprise a tongue and a        groove, wherein this groove is bordered by a lower lip on the        bottom side of the groove and an upper lip on the top side of        the groove hereafter called the lower lip and the upper lip        respectively, and further wherein the distal end of the upper        lip defines or intersects a vertical plane, hereafter called        plane V1;    -   the lower lip is distally longer than the upper lip;    -   there is an interlocking part on the part of the lower lip which        extends past the free end of the upper lip, with a contact        surface which, when coupled, works in conjunction with a contact        surface which is provided on the other panel, whereby these        contact surfaces form a contact zone when coupled, whose center        defines or intersects a vertical plane, hereafter called plane        V2;    -   before the above-mentioned interlocking part, in the direction        of the groove, there is formed a space in the lower lip which is        open on the top side;    -   in the coupled situation, there is a contact zone in the cross        section in which the top side of the tongue makes contact with        the bottom side of the upper lip, whereby the point of this        contact zone which is situated most inwardly defines or        intersects a first vertical plane, hereafter called plane V3,        the most outwardly situated point of this contact zone defines        or intersects a second vertical plane, hereafter called plane        V4, and both planes V3 and V4 define a vertical plane situated        right in between, hereafter called plane V5;    -   the top side of the interlocking part defines a horizontal        level, hereafter called level N1;    -   the bottom side of the part upon which the tongue is provided        and which extends from the tip of the tongue to the interlocking        zone, defines a horizontal level, hereafter called level N2;    -   the levels N1 and N2 define a horizontal level situated right in        between, hereafter called level N3;    -   the average height of the contact zones between the top side of        the tongue and the bottom side of the upper lip define a        horizontal level, hereafter called level N4;    -   the distance between the planes V1 and V2 is at least half of        the distance between the levels N3 and N4;

wherein the floor covering further possesses at least in combination thefollowing characteristics:

-   -   that the panels, and basically also the above-mentioned lips,        are made of fiberboard of the type MDF or HDF;    -   that the coupling means are made such that the panels can be        assembled by pushing them towards one another; and    -   that the above-mentioned space extends to beneath the upper lip,        such that this space is in conformity with at least one of the        following two characteristics:    -   a) that the part of this space which is situated under the level        N3 extends inwardly to at least past the plane V1;    -   b) that the part of this space which is situated under the level        N1 extends inwardly to at least past the plane V5.

When all the above-mentioned criteria are met, an embodiment is obtainedaccording to the invention whereby the above-mentioned space isrelatively large compared to the other parameters on the one hand, and,thanks to the specific application of the MDF or HDF material, thestructure nevertheless remains sufficiently stable on the other hand.The relatively large space which is formed in the lower lip offers theadvantage that the tongue can be located in the groove more easily, aswell as the advantage that the tongue can be made relatively massive.

According to a particular embodiment, this floor covering panel ischaracterized in that the panel is rectangular and in that couplingmeans are formed on both pairs of edges which offer an interlocking inthe horizontal and vertical directions, wherein these coupling means areformed as mentioned above on at least one pair of said edges, andwhereby on at least two edges intersecting at right angles to oneanother, use is made of a groove which is bordered by an upper lip and alower lip respectively, whereby the lower lip each time protrudesfurther than the upper lip, such that two such longer lips meet in atleast one angle of the panel, whereby at least the above-mentioned spacecontinues up to the end of the panel in said angle, in other wordsextends through the far end of the lip standing at right angles. As theabove-mentioned space is made continuous, also a large flexibility canbe guaranteed in the angle concerned, as the interlocking parts of thelongitudinally directed lower lip and the transversely directed lowerlip are then disconnected by this continuous recess.

According to an eight aspect, the invention provides for floor coveringhard panels, whereby these panels are provided with coupling means on atleast two opposite edges made in one piece with the panels, as a resultof which several of such panels can be mutually coupled to one another,whereby these coupling means provide for an interlocking in a verticaldirection perpendicular to the plane of the coupled panels, as well asin a horizontal direction perpendicular to the edges concerned andparallel to the plane of the coupled panels, and whereby:

-   -   the above-mentioned coupling means comprise a tongue and a        groove, wherein the groove is bordered by a lip on the bottom        side and the top side of the groove, hereafter called the lower        lip and the upper lip respectively;    -   the lower lip is longer than the upper lip;    -   there is an interlocking part on the part of the lower lip which        extends past the free end of the upper lip, with a contact        surface which, when coupled, works in conjunction with a contact        surface which is provided on the other coupled panel; and    -   before the above-mentioned interlocking part, in the direction        of the groove, is formed a space in the lower lip which is open        on the top side;

wherein the coupling means are made such that the panels can beassembled by pushing them towards one another while in a generallycommon place, and in that in the bottom side of the part onto which thetongue is provided, and which extends from the tip of the tongue up tothe interlocking zone, is provided a depression, such that thisdepression co-operates with the interlocking part in a position at whichthe tongue is situated in front of the groove. Thus is obtained that,while the tongue is being fit in, the interlocking part is located inthe depression, so that the tongue is better positioned in front of thegroove of the other panel.

Floor coverings consisting of hard panels known until now, and whichallow for a glueless interlocking, do not enable temporary removal ofindividual panels from the middle of the floor covering after the floorcovering has been entirely laid. This is disadvantageous in that it isdifficult to replace damaged panels, as well as impossible to locallyremove the floor covering, for example to work on or in the rough floor,to lay or remove cables under the floor covering, etc. With the knownsystems, the panels always need to be systematically removed from anedge of the floor covering.

According to a ninth aspect, the invention aims to provide floorcovering hard panels, whereby it is possible to remove any coupled panelwhatsoever from an existing floor covering made of coupled panels, andto put it back, without the floor covering having to be systematicallybroken up from an edge of the whole.

According to this ninth aspect, the invention to this end provides for afloor covering hard panel, wherein the panel is provided with couplingmeans on at least two opposite edges made in one piece with the panel,as a result of which several of such panels can be mutually coupled toone another, whereby these coupling means provide for an interlocking ina vertical direction perpendicular to the plane of the coupled panels,as well as in a horizontal direction perpendicular to the edgesconcerned and parallel to the plane of the coupled panels, whereby theabove-mentioned coupling means are made such that two coupled panels,starting from a flat position, can be turned towards one another towardtheir bottom sides over at least a certain angle and this turningmovement makes it possible for said two panels to be removed from inbetween other adjacent coupled panels.

According to a first preferred embodiment, the coupling means are madesuch that the two coupled panels, when they are situated in a floorcovering, may be lifted along their coupled edges, such that there is adisconnection on at least one of the opposite edges that is coupled withadjacent panels.

According to a second preferred embodiment, the coupling means are madesuch that the two coupled panels, when they are situated in a floorcovering, may be lifted along their coupled edges, such that thecoupling, in particular the vertical coupling, is interrupted along theedges concerned and a disconnection along the coupled edges becomespossible.

According to a particularly practical embodiment, the floor coveringpanel is characterized in that the coupling means mainly consist of atongue and a groove, whereby the lip which is situated on the bottomside of the groove is longer than the lip on the top side of the groove,and the interlocking is obtained mainly in the horizontal directionthanks to an interlocking part on the lip situated on the bottom side ofthe groove and an interlocking part working in conjunction with it onthe bottom side of the other coupled panel, whereby these coupling meansmake it possible for the panels to be assembled by means of a turningmovement and whereby, in the coupled position, spaces are provided abovethe first-mentioned interlocking part as well as under thesecond-mentioned interlocking part which allow for a further turningmovement.

The above-described aspects of the invention may occur independently orthey can be mutually combined, in any possible combination, provided theembodiments as described according to the above-mentioned aspects do nothave conflicting characteristics.

DESCRIPTION OF THE DRAWINGS

In order to better explain the characteristics of the invention, thefollowing preferred embodiments are described as an example only withoutbeing limitative in any way, with reference to the accompanyingdrawings, in which:

FIG. 1 schematically represents a hard flooring panel;

FIG. 2 schematically represents a part of a floor covering made of hardpanels shown in FIG. 1;

FIG. 3 represents an embodiment of coupling means of coupled panelsaccording to the invention applied in a floor covering, seen from asection which corresponds for example to section III-III in FIG. 2;

FIG. 4 represents a section according to prior art viewed along lineIV-IV in FIG. 2;

FIG. 5 represents a variant of FIG. 4;

FIGS. 6 to 8 represent the coupling means from FIG. 3 in differentpositions;

FIG. 9 represents a variant of the coupling means from FIG. 3;

FIG. 10 represents another variant;

FIGS. 11 to 13 represent the variant from FIG. 10 in differentpositions;

FIG. 14 represents another variant;

FIG. 15 represents yet another variant;

FIGS. 16 and 17 represent the coupling means of FIG. 15 in two otherpositions;

FIG. 18 represents an angular part of a panel according to theinvention;

FIG. 19 represents a section of another embodiment according to theinvention;

FIG. 20 represents a section of another embodiment of a floor coveringmade of panels according to the invention;

FIG. 21 represents the part indicated by F21 in FIG. 20 on a largerscale;

FIG. 22 represents how the panels of the floor covering from FIG. 20 canbe disconnected and connected respectively;

FIG. 23 represents the part indicated by F23 in FIG. 22 on a largerscale;

FIG. 24 represents a view analogous to that in FIG. 21 for anothervariant;

FIG. 25 represents how the panels of FIG. 24 can be mutuallydisconnected and connected respectively;

FIG. 26 represents the part indicated by F26 in FIG. 25 on a largerscale.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

As represented in FIGS. 1 and 2, the invention concerns hard floorcovering panels 2 from which a floor covering 1 may be formed bycoupling of the panels.

As described in U.S. Pat. No. 6,006,486, it is known that such panels 2can be connected without any glue being required by making use ofcoupling means which, when the panels 2 are rectangular, provide for aninterlocking in a direction R1, perpendicular to the plane of the floorcovering 1, at least on one pair of opposite edges 3-4, and preferablyon both pairs of edges 3-4, 5-6 respectively, as well as in a directionR2 perpendicular to the edges 3-4 or 5-6 concerned, and parallel to theplane of the floor covering 1.

Coupling means can be used which allow for different coupling methods,but preferably coupling by rotating the panels relative to each other aswell as by pushing the panels together while in a generally commonplane. The latter makes it possible for such panels 2 to be coupled toone another in a known manner by first rotating them into one another ontheir edges 3-4, as represented by means of the panel 2A in FIG. 2 witha movement of rotation W1, and by subsequently snapping them together ontheir edges 5-6 by means of a translation motion T1. According to avariant, the connection on the edges 3-4 of the panels 2 concerned, canalso be realized by starting from a position as is schematicallyindicated by reference 2B, and coupling the panel 2 concerned by meansof a translation T2.

Also, while a panel 2A is maintained in the rotated position, afollowing panel 2C can be coupled to the edges 5 and 6 concerned, eitherby means of a translation T3, or by means of a mutual rotation betweenthe panels 2A and 2C, after which both panels 2A and 2C are then turneddown so as to be locked to the preceding row of panels.

As mentioned in the introduction, the present invention providesdifferent new embodiments of coupling means to mutually connect suchpanels 2.

FIG. 3 represents an embodiment according to a first aspect of theinvention.

Also, in this embodiment, the floor covering 1 comprises hard panels 2which are provided with coupling means 7 made in one piece with thepanels 2 on at least two opposite edges, in this case 5-6, so thatseveral of such panels 2 can be mutually connected to one another. Thesecoupling means 7 provide for an interlocking in the direction R1, aswell as R2.

Further, these coupling means 7 have a tongue 8 provided on the edge 5,and a groove 9 provided on the edge 6, in which the tongue 8 fits. Thegroove 9 is hereby bordered on the top side by means of a lip 10,hereafter called the upper lip. At the bottom, it is bordered by a lip11, hereafter called the lower lip, which is longer than the upper lip10, in other words, which extends further than the distal end 12 of thelip 10 in the horizontal direction away from groove 9.

The interlocking in the direction R2 is obtained as the lower lip 11forms an interlocking part 13 with an inwardly directed contact surface14 which can co-operate with an opposite contact surface 15 formed onthe edge 5 when being coupled.

According to the invention, the panel edge 5 which is provided with thetongue 8 is made elastically flexible, whereas the lip 11 is preferablymade rigid, the latter by making it relatively thick, as is clearlyvisible in FIG. 3.

The panel edge 5 is made such that it can elastically bend in severalplaces. Thus, for example, the tongue 8 is flexible, but even moreimportant is that this tongue 8 is preferably situated on a part 16, asrepresented, which is connected to the actual panel 2 via a flexiblezone 17 in the shape of a local constriction or reduced cross-section.

This flexible zone 17 is preferably situated on the place as indicatedin FIG. 3, in other words seen as of the tongue 8, past the contactsurface 15, and said flexible zone 17 has a thickness D1, according tothe direction R1, which is smaller than half the thickness of the panels2 and/or smaller than ⅔ of the thickness D2 of the part 16 upon whichthe tongue 8 is situated.

If the panels 2 are made of fiberboard, of the type MDF or HDF, thethickness D1 is preferably even smaller than 3 mm, and better stillsmaller than 2 mm.

The flexible zone 17 is situated against the top side 18 of the panel 2concerned, which is particularly useful when MDF or HDF board is used,as such materials have a larger density on the outer surfaces, and thusthe thickness on these places can be maximally reduced so as to obtainan optimal flexibility.

Apart from the advantages already mentioned in the introduction, theinvention according to the first aspect also offers the followingadvantageous characteristics:

-   -   As the contact surface 14 is situated relatively high, said        contact surface 14 can be provided in a more vertical position,        without much deviation from the tangential directions B1 and B2        represented in FIG. 3. Thus is obtained a solid interlocking.    -   As the flexibility of the connection is situated in the top side        of the panel, this results in the interlocking being pulled even        more tightly together when a tensile force is exerted on the        panels.    -   In the design of FIG. 3 is created a stress concentration on the        top side of the panel 2, right behind the tongue 8, which        results in a bending. As a consequence, the stress concentration        is transferred to the strongest place of the board. During the        joining, it is practically impossible for forces to be created        in the deepest point of a groove 9, so that it is almost        excluded that splits are created at this deepest point.

According to a second aspect of the invention, which in the givenexample of FIG. 3 is combined with the above-mentioned first aspect, thecoupling means 7 consist at least of first coupling parts formed ofcontact surfaces 19-20 working in conjunction with one another, on thetop side of the tongue 8 and the bottom side of the upper lip 10respectively; second coupling parts formed of contact surfaces 21-22, onthe top side of the lower lip 11 and the opposite part 16 of the otherpanel 2 respectively; and third coupling parts which provide for thehorizontal interlocking situated on the lower lip 11, but further thanthe free end 12 of the upper lip 10, formed of the above-mentionedcontact surfaces 14 and 15. What is special here, is that the thirdcoupling parts are situated between the first and the second ones.

The second coupling parts are preferably situated immediately next tothe third coupling parts. The contact surface 21 is hereby formed of thetop side of the above-mentioned interlocking part 13, whereas thecontact surface 22 is situated precisely opposite to it.

According to the embodiment of FIG. 3, there is a free space 23 underthe tongue 8 which extends from the tip 24 of the tongue 8 up to thethird coupling parts, in other words the contact surface 14.

The coupling means 7 are mainly designed to be provided on one pair ofedges 5-6, whereas coupling means 25 are preferably provided on theother edges 3-4, as represented in FIG. 4 or FIG. 5, which are describedin U.S. Pat. No. 6,006,486 and which make it possible for the panels 2concerned to be assembled along their top edges and, disassembled,respectively at least by means of a movement of relative rotation. Inthe case where the panels 2, as represented, are longitudinal, thecoupling means 7 will preferably be provided on the short edges 5-6.

The above-described arrangement does not exclude, however, that thecoupling means 7 may be provided on both pairs of edges 3-4 and 5-6, oron the longitudinal edges 3-4, whereas another connection is providedfor on the short edges.

Nor is it excluded to provide the panels 2 on merely one pair of edgeswith coupling means, in this case the coupling means 7.

Further, the coupling means 7 are preferably made such that the panels 2with their edges concerned, in this case the edges 5 and 6, can beconnected to one another by pushing the panels 2 freely towards oneanother, as is represented step by step in FIGS. 6 to 8, and as will befurther described into more detail. Moreover, the coupling means 7 aremade such that the edges concerned, in this case the edges 5 and 6, canalso be connected to one another by means of a movement of relativerotation, and disconnected, respectively, as is represented by means ofa dot and dash line in FIG. 3.

The laying of the floor covering 1, with panels 2 containing couplingmeans 7, can then for example, yet not necessarily, be carried out asfollows. In a situation as represented in FIG. 2, the panel 2A is firstconnected with its edge 3 to an edge 4 of already laid panels bypresenting the panel 2A at an angle and by rotating the above-mentionededges 3-4 into one another, so that a connection such as for example inFIG. 4, or, as an alternative, FIG. 5, is created.

Then, the panel 2A can be connected to the preceding panel with atranslation T1, whereby the situations as represented in FIGS. 6 to 8are successively observed on the coupling means 7. It is clear that thisis accompanied by an elastic bending in the tongue 8, and to a largerextent also in the flexible zone 17, whereby the part 16 with thecontact surface 15 finally snaps down behind the contact surface 14.

FIG. 9 represents an embodiment which is realized according to theabove-mentioned third aspect of the invention. The coupling means 26used hereby represent first coupling parts analogous to the couplingmeans 7, formed by contact surfaces 19 and 20, and third coupling partsformed by contact surfaces 14 and 15. What is special in this example,is that the above-mentioned second coupling parts are situated betweenthe first and third ones, and that the second coupling parts consist ofcontact surfaces 27-28 working in conjunction with one another and whichdefine a local contact zone 29 which is situated in the middle orpractically in the middle between the tip 24 of the tongue 8 and thethird coupling parts, in other words the contact surface 14.

As represented in FIG. 9, a bulge or protrusion 30 can be provided inthe lower lip 11 on the contact zone 29.

FIGS. 10 to 13 represent an embodiment for different positions withcoupling means 31 which are in conformity with a fourth aspect of theinvention. The upper lip 10 is hereby longer than the lower lip 11, andthe coupling means which realize the interlocking in the horizontaldirection consist of coupling parts formed of contact surfaces 32-33working in conjunction with one another, which are provided on thebottom side of the upper lip 10, outside the distal end of the lower lip11, and on the opposite part of the edge of the other panel 2respectively.

The coupling means 31 are hereby made such that the connection can berealized by pushing the panels 2 towards one another with the edges 5-6concerned, for example over a base, whereby they systematically fit intoone another, as represented in FIGS. 10 to 12.

As shown in the figures, the tongue 8 has one end 24 which has been madethinner. There is also a free space 35 between the free end 36 of thelower lip 11 and the opposite part 37 under the tongue 8 of the otherpanel 2.

The embodiment of FIGS. 10 to 13 also illustrates a fifth aspect of theinvention, in other words that the edges, in this case the edges 5-6,are provided with coupling means 31 which make it possible for thepanels 2 concerned to be mutually disconnected by rotating them towardstheir bottom sides 38 and towards one another, as is specifically shownin FIG. 13. The above-mentioned space 35 is helpful thereby.

The embodiment of FIGS. 10 to 13 also corresponds to a sixth aspect ofthe invention, wherein the interlocking in the horizontal direction isformed of coupling parts in the shape of a local protrusion 39 in thetop side 40 of the above-mentioned tongue 8, which meshes in a recess 41in the upper lip 10. The upper or top side of the tongue 8 is shown ashaving an arcuate surface area 40 to facilitate separation ordisconnecting of the coupled panels, as seen in FIG. 13. Morespecifically, the arcuate surface 40 engages and rotates over the lowerside of the upper lip 10 of groove 9 to allow a smooth disconnectbetween panels 5 and 6 effected by rotating them towards each other andtowards their bottom sides. The free space 35 also facilitates saidrotation. Moreover, it will be observed in FIG. 10 that the upper liplower side or surface and the lower lip upper side or surface cooperatewith the tongue upper side and the tongue lower side, respectively, whenadjacent panels are coupled so that the coupled panels are kept in thesame general horizontal plane. The upper lip lower side, the lower lipupper side, the tongue upper side and tongue lower side that cooperatewith one another may be referred to as lip upper abutment surface, liplower abutment surface, tongue upper abutment surface and tongue lowerabutment surface, respectively.

FIG. 14 represents a variant which also applies the above-mentionedcharacteristics of the sixth aspect of the invention.

Other particularities of this embodiment, which must not all be combinedaccording to variants which are not represented, consist in that the topside 40 of the tongue 8, with the exception of the local protrusion 39,is mainly parallel to the surface of the floor covering 1, and in thatthe bottom side 42 of the tongue 8 is mainly formed of a smoothly bentsurface which reaches up to the top side 40 of the tongue 8. Also thisembodiment makes it possible for the panels 2 to be assembled by meansof a mainly horizontal movement as well as rotational movement about thecoupled edge.

As seen in FIG. 14, the groove 9 has an innermost point 9 a. The recess41 is located within the portion of the groove 9 which is locatedbetween the innermost point 9 a of the groove and the distal end 36 ofthe lower lip 11. It will also be evident that the bottom side of thetongue 8 at least in the region of the tongue located directlyunderneath the protrusion 39 and underneath the portion of the top sideof the tongue extending from the protrusion 41 to the distal end 8 a ofthe tongue is free from horizontally active coupling parts. It will alsobe evident from FIG. 14 that the protrusion 41 is located at a distanceproximally inwardly from an imaginary vertical transverse planeintersecting the distal tip 8 a of the tongue 8. A portion 40 a of thetop side of the tongue 8 extends generally parallel with the plane ofthe floor panel and forms a contact surface cooperating with the lowerside of the upper lip 10.

FIG. 15 represents a connection with coupling means 43 realizedaccording to a seventh aspect of the invention. It concerns a connectionwhereby:

-   -   the coupling means 43 comprise a tongue 8 and a groove 9,        whereby this groove 9 is bordered on the bottom and top sides,        respectively, by a lip, hereafter called the lower lip 11 and        the upper lip 10, respectively, wherein the distal end 12 of the        upper lip 10 defines (i.e., intersects) a vertical plane,        hereafter called plane V1;    -   the lower lip 11 is longer than the upper lip 10;    -   there is an interlocking part 13 on the part of the lower lip 11        which extends past the free end 12 of the upper lip 10, with a        contact surface 14 which, when coupled, works in conjunction        with a contact surface 15 which is provided on the other panel        2, whereby these contact surfaces 14-15 form a contact zone when        coupled, whose center M1 intersects a vertical plane, hereafter        called plane V2;    -   before the above-mentioned interlocking part 13, in the        direction of the groove 9, is formed an open space 44 in the        lower lip 11 which is open on the top side;    -   in the coupled situation, there is a contact zone in the cross        section in which the top side of the tongue 8 makes contact with        the bottom side of the upper lip 10, whereby the point C3 of        this contact zone which is situated most inwardly intersects a        first vertical plane, hereafter called plane V3, the most        outwardly situated point C4 of this contact zone intersects a        second vertical plane, hereafter called plane V4, and both        planes V3 and V4 define a vertical plane situated right in        between, hereafter called plane V5;    -   the top side of the interlocking part 13 defines a horizontal        level, hereafter called level N1;    -   the bottom side of the part 16 upon which the tongue 8 is        provided and which extends from the tip 24 of the tongue 8 to        the interlocking zone, defines a horizontal level, hereafter        called level N2;    -   the levels N1 and N2 define a horizontal level situated right in        between, hereafter called level N3;    -   the average height of the contact zone between the top side of        the tongue 8 and the bottom side of the upper lip 10 define a        horizontal level, hereafter called level N4;    -   the distance between the planes V1 and V2 is at least half of        the distance between the levels N3 and N4.

This floor covering 1 is special in that it provides at least thecombination of the following characteristics:

-   -   that the panels 2, and basically also the above-mentioned lips        10-11, are made of fiberboard of the type MDF or HDF;    -   that the coupling means 43 are made such that the panels 2 can        be assembled by pushing them towards one another; and    -   that the above-mentioned space 44 extends to beneath the upper        lip 10, such that this space 44 is in conformity with at least        one of the following two characteristics:    -   a) that the part of this space 44 which is situated under the        level N3 extends inwardly to at least past the plane V1;    -   b) that the part of this space 44 which is situated under the        level N1 extends inwardly to at least past the plane V5.

Thanks to this specific combination there is obtained a space 44 whichacts as a depression in relation to the other dimensions extending overa relatively large distance in the direction R2, as a result of whichthe advantages mentioned in the introduction are obtained. In spite ofthe relatively large depression and, consequently, the fact that thelower lip 11 is relatively thin, the rigidity remains neverthelesssufficient thanks to the use of MDF or HDF as a base material, which hasa layered fibrous structure.

The distance between the levels N1 and N2 is preferably smaller than ⅓of the distance between the levels N2 and N4. Thus, the obstructionformed by the interlocking part 13 while the panels are being pushedtogether, is restricted to a minimum, as a result of which the panels 2can smoothly slide into one another.

Further, the intersection P4 between the plane V4 and the bottom side ofthe tongue 8 is situated beneath level N1, seen from a cross section,and better still beneath level N3. The tongue 8 thus obtains arelatively large thickness, which improves its rigidity. Further, it iseven possible for the section P5 between the plane V5 and the bottomside of the tongue 8 to be situated beneath level N1, and better stillbeneath level N3.

In particular, the section P3 between the plane V3 and the bottom sideof the tongue 8 could be situated beneath level N1, and better stillbeneath level N3.

According to a preferred characteristic of the invention, the part ofthe above-mentioned space 44 situated under the plane N3 would extend atleast inwardly up to the vertical plane V6 which is determined by thetip 24 of the tongue 8.

In the case where the panels 2 are rectangular and coupling means areformed on both pairs of edges 3-4 and 5-6 which provide for a verticaland a horizontal interlocking, whereby both edges 4 and 6 have a lowerlip 11, 11A respectively, which is longer than the upper lip 10, atleast the above-mentioned space 44 is preferably made continuous up tothe end of the panel 2, as represented in FIG. 18, in the corner 45, inother words it extends through the far end of the square lip 10A, inparticular the interlocking part 13A thereof. As the space 44 isrelatively large on the one hand, and this space 44 extends through theinterlocking part 13A on the other hand, and the interlocking parts 13and 13A are disconnected from one another, a particularly flexible angleis obtained, which makes it easier to assemble the panels.

FIG. 19 illustrates an eighth aspect of the invention, whereby adepression 46 is provided in the bottom side of the tongue 8, such thatin the mutual position of the two panels 2 as represented in FIG. 19,the tongue 8 is better positioned in front of the groove.

It should be noted that in all the above-mentioned embodiments, thecontact surfaces providing for the horizontal interlocking arepreferably directed slantingly in relation to the plane of the floorcovering 1. This does not exclude, however, that according to a variant,one or both contact surfaces can also be directed perpendicular to theplane of the floor covering. The contact surfaces can also be bent assuch, whereby the tangent line in the middle of the contact zonedetermines the above-mentioned gradient.

In the case where these contact surfaces, or their tangent line, aredirected slantingly, they preferably extend in a direction which istangential or almost tangential to a circle, whose center is situated ona point of rotation around which the panels 2 can be turned apart. Asindicated in FIG. 3, this means that the gradient or direction B1 of thecontact surfaces deviates only little from the gradient of the tangentB2 onto the circle C.

In order to provide for a snap-in effect, the direction B1 pertaining tothe contact surfaces preferably does deviate from the direction of theabove-mentioned tangent B2 and is directed inwardly, such that a snap-ineffect is created when the panels are rotated into one another, wherebythe above-mentioned direction B1 deviates 30° at the most from theabove-mentioned tangential direction B2.

What precedes can be applied in all the rotatable embodiments describedabove, also in the embodiments whereby the panels 2 are rotated apart byturning them down.

The coupling means which are realized according to one or several of thefirst eight aspects of the invention are all particularly suitable to beprovided on edges 3-4 and/or 5-6, whereby it must be possible toassemble the panels 2 by shifting them.

In the case where the panels 2 are rectangular, in other words square orlongitudinal, they are preferably provided with coupling parts on allfour edges 3-4 and 5-6 which allow for a vertical and a horizontalinterlocking, whereby coupling means as described in one or several ofthe above-mentioned first eight aspects are then provided on at leasttwo opposite edges 3-4 or 5-6.

In the case where the panels 2 are rectangular, the new coupling meansare preferably provided at least on the short edges 5-6. Further,coupling means are then preferably provided on the long edges 3-4 whichallow for an assembly, disassembly respectively by means of a movementof rotation, which can be of a known nature or which can also be madeaccording to any of the above-mentioned eight aspects.

FIGS. 20 to 23 show an embodiment according to a ninth aspect of theinvention. According to this ninth aspect, it concerns floor coveringhard panels 2, wherein these panels 2 are provided on at least twoopposite edges, in the case of elongated panels 2 preferably on thelongitudinal edges 3-4, with coupling means 7 made in one piece with thepanels 2, so that several of such panels 2 can be mutually connected toone another to form floor covering 1, whereby these coupling means 7provide for an interlocking in a direction R1, perpendicular to theplane of the coupled panels, as well as in a direction R2 perpendicularto the edges 3-4 concerned and parallel to the plane of the coupledpanels, whereby the above-mentioned coupling means 7 are made such thattwo connected panels 2 can be turned about their coupled edges towardsone another toward their bottom side, starting from a flat position,over at least a certain angle on the one hand, whereby this turningmovement makes it possible for the two above-mentioned panels 2 to beremoved from between other adjacent panels 2D and 2E.

Moreover, according to the embodiment of FIGS. 20 to 23, the couplingmeans 7 are made such that, as represented in FIG. 22, they make itpossible for the two panels 2 to be lifted along their coupled edges3-4, from a flat position, such that there is a disconnection on atleast one of the opposite edges which provide for the connection withthe adjacent panels 2D and 2E. Thus, the panels 2 can be removed from anexisting floor covering 1 by first lifting them as mentioned above andby subsequently turning the left panel 2 from FIG. 22 up, as representedby means of a dot and dash line, so that the left panel 2 of FIG. 22 canbe removed. Next, also the right panel 2 can be removed. The initiallifting of the panels 2 can take place in any way whatsoever, forexample by means of a suction cup or by sticking a hook or such throughan opening made in the floor covering, for example a bore hole.

FIGS. 20 to 26 represent variants whereby the coupling means 7 are madesuch that they make it possible for the two panels 2 to be lifted, froma flat position, along their coupled edges 3-4, such that theconnection, in particular the vertical connection on the edges 3-4concerned is undone. In this case, it is not necessary to disconnect thepanels 2D and/or 2E first in order to disconnect the two panels 2.

Both in the embodiment of FIGS. 20 to 23 and in the one of FIGS. 24 to26, the coupling means 7 mainly consist of a tongue 8 and a groove 9,whereby the lip 11 which is situated on the bottom side of the groove 9is longer than the lip 10 on the top side, and the interlocking ismainly obtained in the horizontal direction by means of an interlockingpart 13 on the lip 11 and an interlocking part 47 on the bottom side ofthe other panel 2 working in conjunction with it, whereby these couplingmeans 7 make it possible for the panels 2 to be assembled by means of aturning movement, and whereby, in the coupled position, there are spaces48-49 above the first-mentioned interlocking part 13, as well as underthe second-mentioned interlocking part 47, which allow for a furtherturning.

Practically, the above-mentioned interlocking parts 13-47 are positionedsuch that a lateral play S is created during the above-mentioned furtherturning, as is schematically represented in FIG. 21, so that a certainfreedom of movement is obtained which is desirable in order to removethe panels 2 from between the fixed panels 2D and 2E.

In the embodiment of FIGS. 24 to 26, this lateral play S, as well as thedesign of the tongue 8 and the groove 9, are selected such that theright panel 2, in the situation of FIG. 26, comes loose so to say andcan simply be removed from the left panel 2.

In particular, the distance Z1 between the tip of the tongue 8 and theinterlocking part 47 situated on the same edge is smaller than or equalto the distance Z2 between the tip of the lip 10 bordering the top sideof the groove 9 and the interlocking part 13 situated on the lip 11bordering the bottom side of the groove 9.

It should be noted that in the embodiments of FIGS. 20 to 26, the tongue8 is preferably made such that it can make a movement of rotation in thegroove 9, as said tongue 8 is more or less round, as represented inFIGS. 20 to 23, or because it is relatively short, as represented inFIGS. 24 to 26.

As represented, coupling means are preferably provided both on the shortedges and on the longitudinal edges which allow for an interlocking bothin the vertical and in the horizontal direction, whereby they can all bemade such that they allow for a connection and disconnection asdescribed above with regard to FIGS. 20 to 26. It is also possible toapply the coupling means represented in these figures only on thelongitudinal edges, whereas coupling means with another shape areapplied on the short sides, for example as represented in FIG. 4.

The invention is by no means limited to the above-described embodimentsrepresented in the accompanying drawings; on the contrary, such a floorcovering can be made in different shapes and dimensions while stillremaining within the scope of the invention.

The invention claimed is:
 1. A floor covering, comprising a plurality offloor panels; each panel comprising coupling elements on at least twoopposite edges made in one piece with the panel, said coupling elementsenabling said panels to be mutually coupled to one another, wherein saidcoupling elements enable interlocking of the edges in a directionperpendicular to a plane of the coupled panels, as well as in adirection perpendicular to the edges concerned, and parallel to a planeof the coupled floor panels; said coupling elements comprising a tongueand a groove, said groove being bordered by an upper lip and a lowerlip, and said coupling elements comprising coupling parts which enableinterlocking of the edges in a horizontal direction; said upper andlower lips having lip upper and lip lower abutment surfaces,respectively, and said tongue having tongue upper and tongue lowerabutment surfaces on an upper and lower side of the tongue,respectively; wherein said upper lip extends beyond said lower lip;wherein in coupled condition of two of such panels, said lip upper andsaid lip lower abutment surfaces in a vertical direction engagerespectively the tongue upper and tongue lower abutment surfaces,thereby keeping the coupled panels in a same general plane; and whereinsaid coupling elements are configured such that two adjacent coupledpanels are mutually disconnectable by rotating their bottom sidestowards one another, said configuration including an arcuate area on atongue upper side that engages and rotates relative to the lip upperabutment surface during uncoupling of the panels and a free spacebetween a free end of the lower lip of one panel and an opposing partunder the tongue of the other panel.
 2. The floor panel of claim 1,wherein the panel is formed of a board made of a wood base material. 3.The floor panel of claim 1, wherein said board is formed of a materialselected from the group consisting of MDF (Medium Density Fibreboard)and HDF (High Density Fibreboard).
 4. The floor panel of claim 1,including a decorative layer.
 5. The floor panel of claim 4, whereinsaid decorative layer is selected from the group consisting of printedpaper layer, veneer, cork and strips of wood.
 6. The floor panel ofclaim 1, wherein said coupling parts which provide the interlocking inthe horizontal direction comprise a protrusion at an upper side of thetongue, which co-operates with a recess in the upper lip.
 7. The floorpanel of claim 6, wherein said protrusion is a local protrusion and thusextends over only a part of the upper side of the tongue.
 8. The floorpanel of claim 7, wherein said tongue has a distal end and a proximalend, wherein said protrusion is located at a distance from said proximalend and said arcuate area of said tongue is located between said distalend and said protrusion.
 9. A floor covering, comprising: a plurality offloor panels: each floor panel comprising two pairs of opposite edges;wherein the first pair of opposite edges comprises coupling elementsmade in one piece with the panel, said coupling elements enablingseveral of such panels to be mutually coupled to one another; whereinthe coupling elements enable interlocking of the edges in a directionperpendicular to a plane of the coupled panels, as well as in adirection perpendicular to the edges concerned, and parallel to a planeof the coupled panels; said coupling elements comprising a tongue and agroove, said groove being bordered by an upper lip and a lower lip, andsaid coupling elements comprising coupling parts which provide forinterlocking of the edges in the horizontal direction; wherein thesecond pair of opposite edges comprises second coupling elements made inone piece with the panel, said second coupling elements enabling severalof such panels to be mutually coupled to one another; wherein saidsecond coupling elements enable interlocking of the edges in a directionperpendicular to a plane of the coupled panels, as well as in adirection perpendicular to the edges concerned, and parallel to a planeof the floor panels; said second coupling elements comprising a tongueand a groove, said groove being bordered by an upper lip and a lowerlip, and said second coupling elements comprising coupling parts whichenable interlocking of the respective edges in the horizontal direction;said upper and lower lip of said groove of said second coupling elementshaving lip upper and lip lower abutment surfaces, respectively, and saidtongue of said second coupling elements having tongue upper and tonguelower abutment surfaces on an upper and lower side of the tongue,respectively; wherein at said second pair of opposite edges said upperlip extends beyond said lower lip; wherein in coupled condition of saidsecond coupling elements, said lip upper and said lip lower abutmentsurfaces in a vertical direction engage respectively the tongue upperand tongue lower abutment surfaces, thereby keeping respective coupledpanels in a same general plane; and wherein at said second pair ofopposite edges said second coupling elements are configured such thattwo coupled panels are mutually disconnectable by rotating their bottomsides towards one another, said configuration including inclined lockingsurfaces provided at said coupling parts which enable interlocking inthe horizontal directions and a space between a free end of the lowerlip of one panel and an opposing part of the other panel.
 10. The floorpanel of claim 9, wherein the panels are rectangular and have alongitudinal form, such that they have long edges and short edges;wherein the first pair of opposite edges form the long edges; andwherein the second pair of opposite edges form the short edges.
 11. Thefloor panel of claim 10, wherein the coupling elements at the long edgesare configured such that they enable assembly, disassembly respectivelyby means of a movement of rotation of one panel relative to the other.12. The floor panel of claim 10, wherein the panel is formed of a boardmade of a wood base material.
 13. The floor panel of claim 9, whereinsaid board is formed of a material selected from the group consisting ofMDF (Medium Density Fibreboard) and HDF (High Density Fibreboard). 14.The floor panel of claim 9, including a decorative layer.
 15. The floorpanel of claim 14, wherein said decorative layer is selected from thegroup consisting of printed paper layer, veneer, cork and strips ofwood.
 16. The floor panel of claim 9, wherein at said second pair ofopposite edges, said second coupling elements which provide theinterlocking in the horizontal direction comprise a protrusion at anupper side of the tongue, which co-operates with a recess in the upperlip.
 17. The floor panel of claim 16, wherein said protrusion is a localprotrusion and thus extends over only a part of the upper side of thetongue.
 18. The floor panel of claim 17, wherein said tongue of saidsecond coupling elements has a distal end and a proximal end, whereinsaid protrusion is located at a distance from said proximal end.